From this comes [David Keith’s] daring idea about crops. Since shading the sun doesn’t remove any greenhouse gases from the atmosphere, why not try to make use of that greenhouse effect? Keith argued that in a future world with more carbon dioxide in the atmosphere, climate models suggest that adding the right amount of sulfur to the upper atmosphere wouldn’t just cool the planet, but would actually increase rainfall in, for example, India.

There’s an old engineer’s saw that says, “Fast, cheap, and good. Pick two.” Solving climate change is this type of problem, and Keith’s solution strikes me as one from the fast and cheap bin. Why those two? It ignores the other effects of increased carbon dioxide in the atmosphere, namely ocean acidification.